1. Field of the Invention
The present invention generally relates to current-steering digital-to-analog converters and, more particularly, to a folded R-2R ladder current-steering digital-to-analog converter.
2. Description of the Prior Art
High speed current-steering digital-to-analog converters are based on a current-steering structure, which enables direct load driving without the need for a high speed amplifier. Current-steering digital-to-analog converters can be generally classified according to four types of main structures: (1) binary-weighted array; (2) segmented array; (3) R-2R ladder; and (4) partially segmented. Among those, the R-2R ladder type is the simplest and most power efficient.
A conventional current-steering digital-to-analog converter is shown in FIG. 1, which is commonly used as a sub-circuit in a partially segmented current-steering digital-to-analog converter; the reason for such popularity being its structural simplicity. In FIG. 1, the converter includes an end current-steering circuit 10 and N-1 R-2R current-steering circuits 20, forming an N-bit R-2R ladder current-steering digital-to-analog converter. It requires N current steering circuits and N current sources, and each node in the R-2R ladder is electrically connected to only one corresponding current source. Although such converters are frequently used as sub-circuits, they are limited to the application aspect. Few researches have been done that is directed to reducing power consumption and the number of passive components in the R-2R ladder current-steering digital-to-analog converter. Therefore, there is a need for a R-2R ladder current-steering digital-to-analog converter with reduced footprint and power consumption.